Over the past couple of years, two hockey “enforcers” — players whose primary job is to slug opponents on the ice — have been diagnosed with chronic traumatic encephalopathy (CTE), a degenerative brain disease found in victims who have suffered repeated blows to the head. Now, alarming new research reveals that you don’t have to be a hockey fighter to put yourself at risk of brain disease.

Neuropathologists at the Boston University Center for the Study of Traumatic Encephalopathy examined the brain of Rick Martin, a seven-time NHL All-Star who played from 1971 through 1981, mostly with the Buffalo Sabres. Martin died of a heart attack, at 59, in March (CTE can only be diagnosed post-mortem). They found that Martin, who was not a frequent fighter, had stage 2 (of 4) CTE. During his life, Martin did not suffer from any of the usual CTE symptoms, such as loss of cognitive abilities, impulsive behavior or depression. Still, the mere presence of CTE is troubling, since the disease could have worsened if Martin had lived longer.

A string of recent events has caused the National Hockey League (NHL), which starts its 2011-12 season Thursday night, to rethink its player safety rules. Martin’s diagnosis will only add more pressure for reform. In January, NHL commissioner Gary Bettman revealed that concussions were on the rise, though he said the increase seemed to be caused by inadvertent contact, rather than intentional head contact from another player. The sport’s star attraction, Sidney Crosby of the Pittsburgh Penguins, missed the second half of last season due to hits he took to the head. After suffering a concussion, Crosby had trouble concentrating, and was even afraid to drive a car. His return is still uncertain.

This summer, the death of three enforcers highlighted the potential link between head trauma and mental illness. Wade Belak, a recently-retired defenseman for the Nashville Predators, died of an apparent suicide on August 31. Just two weeks before that, Rick Rypien, the former Vancouver Canucks player who had just signed a contract with the Winnipeg Jets, and had a long struggle with depression, also killed himself. In May Derek Boogaard of the New York Rangers, who had a history of substance abuse problems, died of an accidental of painkillers and alcohol. The Boston University researchers are studying Boogaard’s brain; the results are pending.

While you can’t draw definite conclusions about the root cause of these tragedies, the evidence is disturbing. The Boston University lab has previously diagnosed two former NHL enforcers with CTE: Bob Probert, who died in 2010, at 45, from heart disease, and Reggie Fleming, who passed away in 2009, at 73. Fleming had suffered from dementia and other worsening CTE symptoms for 30 years.

What lessons should we draw from the diagnosis of Martin, who played left wing, rather than pugilist, on the ice? “The brain doesn’t know the source of its hits,” says Dr. Robert Stern, co-director of the Boston University lab. “It doesn’t know the difference between a fist to the face or check to the board.”

Martin’s only known concussion occurred during a 1977 game. It was an ugly one: he hit his head on the ice, causing convulsions. Martin was not wearing a helmet. In fact, he wore a helmet only in the last four years of his career, after he suffered that injury.

In addition to this known concussion, it’s virtually guaranteed that Martin received multiple subconcussive blows to the head, which can cause just as much long-term brain damage as major concussive episodes. Plus, in hockey, body checks can lead to head trauma. “A quick jolt to the body can result in a movement of the brain inside the skull,” Stern says. “Checks can also cause the head to fall to the ice, or to hit against the boards.”

While Stern and his team have diagnosed CTE only in pro hockey players, a wider subset could be at risk. In football, another sport in which frequent head shots has been linked to brain damage, CTE has been found in the brains of high school and college players. “It’s time to consider eliminating any hits to the head in youth hockey,” says Stern. “We don’t want to destroy the game of hockey. We want to make is safer for athletes of all ages.”

Sean Gregory is a staff writer at TIME. Find him on Twitter at @seanmgregory. You can also continue the discussion on TIME’sFacebook page and on Twitter at @TIME.